Chi-Wai Chow

WDM extended reach passive optical networks using OFDM-QAM

In order to reduce the cost for delivering future broadband services, network operators are inclined to simplify the network architectures by integrating the metro and access networks into a single system. Hence, extended reach passive optical networks (ER-PONs) have been proposed. ER-PON usually has four new features: high data rate in both upstream and downstream signals (>1 Gb/s); reach extension to >100 km; a high split ratio (>100); and using wavelength division multiplexing (WDM). In this work, we propose and demonstrate a highly spectral efficient ER-PON using 4 Gb/s OFDM-QAM for both upstream and downstream signals, while achieving a high split-ratio of 256. The ER-PON employs optical components optimized for GPON (bandwidth of approximately 1 GHz) and reaches 100 km without dispersion compensation. Numerical analysis using 16, 64 and 256-QAM OFDM are also performed to study the back-to-back receiver sensitivities and power penalties at different electrical driving ratios.

Rayleigh noise mitigation in long-reach hybrid DWDM-TDM PONs

Feature Issue on Passive Optical Network Architectures and TechnologiesAn architecture employing a centralized light source and reflective modulator at the customer is proposed and demonstrated for a long-reach, hybrid dense wavelength division multiplexed (DWDM)-time-division multiplexed (TDM) passive optical network (PON). Impairments to the upstream channel caused by Rayleigh backscattering in the network are mitigated using a dual-feeder-fiber approach in conjunction with a novel detuned filtering and spectral-broadening scheme. The experimental results show that the network, with a total reach of 116km and an upstream bit rate of 10Gbits/s, can support up to 256 customers on each TDM PON. The potential performance improvements obtainable from an optimized architecture are also discussed.

Studies of OFDM signal for broadband optical access networks

Using orthogonal-frequency-division-multiplexing (OFDM) format for passive optical network (PON) is a subject of great interest for recent research works. OFDM signal has high spectral efficiency, high tolerance to the fiber chromatic dispersion and the high flexibility on both multiple services provisioning and dynamic bandwidth allocation. In this paper we study the use of OFDM signals for optical access networks, including carrier distributed PON, heterogeneous optical wired/wireless network and a 100 Gb/s OFDM-PON. We first quantify the performance of the OFDM signal when subjected to the noise produced by two different Rayleigh backscattering (RB) components that are present in the carrier-distributed PON. Then, based on these results, we also study the possibility of using OFDM for signal remodulation in a long-reach (LR)-PON. We propose carrier-distributed OFDM PONs using a dual-feeder fiber architecture and wavelength-shifting to mitigate the RB noise. Afterwards, we propose heterogeneous optical wired/wireless access networks, combining 10 Gb/s PON and 10 Gb/s OFDM radio-over-fiber (ROF) network. Finally, we propose a 100 Gb/s OFDM-PON using subcarrier multiplexing (SCM).

Signal Remodulation of OFDM-QAM for Long Reach Carrier Distributed Passive Optical Networks

The passive optical network (PON) using orthogonal frequency-division multiplexing (OFDM) is a subject of many research works recently. The OFDM signal is especially good for long reach (LR)-PON due to its high tolerance to chromatic dispersion and high spectral efficiency. We study, for the first time, the possibility of using OFDM for signal remodulation in LR-PONs. Three different colorless optical networking unit (ONU) architectures, electroabsorption modulator-based, reflective semiconductor optical amplifier-based and injection-locked Fabry-Perot laser diode-based ONUs, are tested and compared. Error-free operations are achieved in 100-km fiber transmission without dispersion compensation.

100 GHz ultra-wideband (UWB) fiber-to-the-antenna (FTTA) system for in-building and in-home networks

Fiber-to-the-antenna (FTTA) system can be a cost-effective technique for distributing high frequency signals from the head-end office to a number of remote antenna units via passive optical splitter and propagating through low-loss and low-cost optical fibers. Here, we experimentally demonstrate an optical ultra-wideband (UWB) - impulse radio (IR) FTTA system for in-building and in-home applications. The optical UWB-IR wireless link is operated in the W-band (75 GHz - 110 GHz) using our developed near-ballistic unitraveling-carrier photodiode based photonic transmitter (PT) and a 10 GHz mode-locked laser. 2.5 Gb/s UWB-IR FTTA systems with 1,024 high split-ratio and transmission over 300 m optical fiber are demonstrated using direct PT modulation.

Rayleigh Noise Reduction in 10-Gb/s DWDM-PONs by Wavelength Detuning and Phase-Modulation-Induced Spectral Broadening

A novel scheme for reducing Rayleigh beat noise in centralized light source dense wavelength-division-multiplexed passive optical networks is demonstrated using an optimized channel-detuned optical filtering of 30 GHz and phase-modulation-induced spectral broadening of a 10-Gb/s upstream nonreturn-to-zero (PM-NRZ) signal. The required optical-signal-to-Rayleigh-noise-ratio (OSRNR), characterized experimentally, can be reduced by up to 16 dB while retaining negligible transmission penalty over 20-km single-mode fiber without dispersion compensation. Numerical analysis is performed to study the tradeoff between OSRNR improvement and attenuation of the PM-NRZ signal as a function of different channel detuning and center wavelength suppressions

Investigation of 4-ASK modulation with digital filtering to increase 20 times of direct modulation speed of white-light LED visible light communication system

In this demonstration, we propose and experimentally investigate the quaternary-amplitude-shift-keying (4-ASK) modulation with digital filtering to enhance the direct modulation speed of white-light light-emitting-diode (LED) in visible light communication (VLC) system. Here, an ordinary LED commercially available for lighting application with a direct modulation speed of 1 MHz is used. Data rate of 20 Mbit/s can be achieved in a 1 m free space transmission without using optical blue filter. In the previous studies, the transmission rate of LED VLC could only be increased by 2 to 10 times of the direct modulation speed of the white-light LED if using electrical equalization only. Moreover, the adaptive-controlled FIR filter makes the system closer to the matched filtering condition for reducing the inter-symbol-interference (ISI) for the LED VLC. A recorded 20 times enhancement of the direct modulation speed of white-light LED VLC system is demonstrated by using digital filter only and without using optical blue filter.

Polarization-independent DPSK demodulation using a birefringent fiber loop

A robust polarization-independent technique for demodulating optical differential phase-shift-keying (DPSK) signals using a birefringent-fiber-loop (BFL) is proposed and demonstrated. The BFL has a differential group delay between its fast and slow optical axes, providing interference which allows the phase modulation to be converted to intensity modulation and then directly detected by a photodiode. Error-free bit-error-rate measurements and clear demodulated eyes were observed. The temperature stability of the scheme improves with the bit rate of the DPSK signal.

In-line channel power monitor based on helium ion implantation in silicon-on-insulator waveguides

We propose and demonstrate an in-line channel power monitor (ICPM) based on helium ion implanted silicon waveguides. The implanted waveguide can detect light at below-bandgap wavelengths (1440-1590 nm) which are normally not detectable by silicon. We study the enhanced photoresponse of helium ion implanted samples which were annealed at 200 degC, 300 degC, or 350 degC for different durations. Optical absorption and photodetector current measurements were performed for each sample. The ICPM can provide the same function as a waveguide tap coupler and a hybrid-integrated conventional photodiode

Real-time white-light phosphor-LED visible light communication (VLC) with compact size

In this demonstration, we first demonstrate a real-time phosphor-LED visible light communication (VLC) system with 37 Mbit/s total throughput under a 1.5 m free space transmission length. The transmitter and receiver modules are compact size. Utilizing our proposed pre-equalization technology, the ~1 MHz bandwidth of phosphor LED could be extended to ~12 MHz without using blue filter. Thus, the increase in bandwidth would enhance the traffic data rate for VLC transmission. The maximum bit-rate achieved by the VLC system is 37 Mbit/s, and a video transmission at 28.419 Mbit/s is demonstrated using the proposed VLC system. In addition, the relationships of received power and signal performance are discussed and analyzed.